The present invention relates to the fabrication of load bearing grate structures typically employed, for example, in commercial and industrial floor, platform and system construction. In another aspect, the present invention relates to an at least three-piece grating system wherein grate structures of load bearing capacity can be efficiently constructed in an interlocking fashion which provides improved structural integrity as compared to multi-piece grate articles which have heretofore been available. In a still further aspect, this invention relates to a method of construction for producing grating articles from individual components which result in improved structural integrity of the grating as a result of the interaction of the components when assembled.
Load bearing grate structures, i.e., structures comprising longitudinal span bars fabricated to support commercial and industrial loads tied together with transverse tie bars, have been conventionally produced from a variety of materials, including wood, metals (such as steel or aluminum, etc.), and more recently, plastic materials, and in particular fiber reinforced plastic resins. In the latter case, "one-piece" grating structures have been fabricated wherein the longitudinal span bars and transverse tie bars are formed integrally during the molding process. In more conventional grating articles, however, the longitudinal span bars must be assembled, usually in parallel, using the transverse tie bars. In the past this assembly has been effected through use of welds or bonding materials as was appropriate for the particular materials from which the grate was being fabricated. In addition to such bonding at the junction between longitudinal span bars and transverse tie bar members, metal stakes and pins have been driven through the span bars and into the tie bars at the junction therebetween to form a mechanical bond therebetween. More recently, thermoplastic spacers in the form of a sleeve over the tie bars have been used in order to maintain spacing between longitudinal span bars. These prior art methods, in addition to being time consuming from a fabrication standpoint, have other drawbacks. For example, the use of metal stakes or pins to form a mechanical connection between span bars and tie bars produces a fracture of the material through which they are driven. This fracture is at precisely the point in the structure where maximum stress occurs under load. Thermoplastic spacers avoid this problem but are subject to deformation, thereby allowing shifts in the relationship between span bar and tie bar to occur under loading conditions. Further, when the grating structure is applied during construction, the use of such spacers becomes disadvantageous since the cutting of an aperture through the grate structure or other shaping of the sides of the grate structure allow the spacers to dislodge from their position on the tie bars, thus abrogating their effectiveness as mechanical locators for the span-tie bar intersection.
Thus, a more economical and efficient means for effecting a mechanical lock between tie bars and longitudinal span bars in grating structures is desirable.